This invention relates to back rests or back supports for a chair. More particularly, this invention relates to one-piece back supports for a chair, such as an office chair. Yet more particularly, this invention relates to one-piece back supports or back rests for a chair having a unique configuration and arrangement of component parts which make it economical to manufacture, and which provide enhanced safety in use and mitigation of failure modes when a chair using the invention is abused or is occupied by larger person.
Conventional chair back rests comprise, from back to front, a vertical support which is attached in some fashion to, the back side of a backing member. The backing member then has located on its remaining front side, a pad. The vertical support holds the backing member in place and supports the back or dorsal side of an occupant of the chair. The pad, placed between the backing member and an occupant of the chair, provides comfort and support to the chair's user.
Conventional chair back rests as described above have shown a particularly unfortunate failure mode, especially when used by larger persons. When a large or heavy person leans backward in a conventional chair, substantial force is exerted against the back support. The backward force, generally being exerted against the top and upper portion of the back support, tends to bend or leverage the upper portion of the back support against the verticle support member. Because there is no restraining force applied against the lower portion or base of the back rest, the back rest is inherently leveraged, bent, or pivots against its verticle support at its structurally weakest point. Conventional back supports, generally being supported in their middle on their back side (i.e., the side away from the chair user) tend to break in what has been referred to as a "half moon" failure mode in response to this force. The "half moon" refers to the shape of a crack or break in the backing member. Such a failure mode, if sudden and complete, potentially permits the vertical support member to pass through the backing member and possibly injure the user.
The present invention mitigates one of the possible failure modes of conventional chair back supports in utilizing a unique arrangement of vertical support and backing member. The aforementioned "half-moon" failure mode is mitigated because the structurally strongest portion of the present invention is located where this failure mode is likely to occur. In addition, the present invention, in a preferred embodiment, permits the utilization of relatively inexpensive, composite materials.